1. Field of the Invention
This invention relates to vehicle winches and in particular it relates to a load limiting control to automatically shut down the winch motor in the event of an overload condition.
2. Background Information
Vehicle winches are produced in a variety of sizes and configurations. The winches are rated at an individual capacity, generally being listed as a pulling capacity such as 6,000 pounds, 10,000 pounds and so forth. The winch is driven by a motor, most often electric, which receives its power from the vehicle battery. The winch motor has sufficient torque to drive the winch at the rated capacity and the rated capacity is thus at a level at which the winch will continue to perform to reel cable onto the drum with a load attached to the cable. Of necessity, the motor must have the capability to provide more torque than required so that the motor is not stalled before the rated capacity of the winch is attained. It is therefore possible to overload the winch by trying to pull a load over the rated capacity by the continued application of power to the motor. It is recognized that winches without load limiting devices attached to a load beyond the capacity of the winch are readily overloaded by continued application of power to the motor. A severe overload condition would be the condition under which the drive motor stalls.
Many winches are therefore provided with load limiting devices that shut off the power to the drive motor when an overload condition occurs. An example of such a device is the Winch With Shut-Off Load Limiter as disclosed in the commonly assigned U.S. Pat. No. 4,873,474. The device utilizes a hall effect switch to shut off the power to the drive motor when an overload condition occurs. The conductor to the motor is passed through a torroid which concentrates the magnetic flux produced by the current flow. The flux increases with current draw (flow) and is thus related to the power input to the winch.
The hall effect switch receives a controlled voltage input that is independent of the torroid. The output of the hall effect switch trips the motor switch only when the combined voltage and magnetic flux through the torroid reaches a determined level. Thus, the combination offers the means to establish a load limit shut off. However, the motor's pulling capability and the torroid flux output are not predictable from motor to motor. Numerous variables enter into the equation and in the design of the prior load limiter of U.S. Pat. No. 4,873,474, these variables were accommodated by altering the controlled voltage input to the hall effect switch. Conceptually, lowering the voltage input required increased flux to open the switch and raising the voltage required less flux to open the switch. Thus, for each motor, the current draw on the motor was established as that which would produce the pulling force limit. Applying that current through the torroid then established the flux level for tripping the motor switch. With that flux level input to the hall effect switch, the voltage input was varied until the current output at that flux level would open the motor switch. That voltage input was then fixed and conceptually the motor would shut down anytime that the motor current generated the established flux level.
The problem encountered with the above design was that the hall effect switch did not reliably perform at the different voltage input settings. A variable as much as plus or minus 1,000 pounds was experienced and had to be built into the design parameters for the winch. A plus or minus 500 pound variable is encountered without the variable of the hall effect switch and thus in order to make sure that the pulling load of a winch was not exceeded, a 3,000 pound variable had to be accounted for. A motor which was represented to have a 10,000 pound load pulling capability had to be set for automatic shut off at 11,500 pounds which, because of the plus or minus 1,500 pound variable, had to be capable of pulling a 13,000 pound load.
It is an objective of this invention to reduce the variable range for the load limiter and in particular to effectively remove the variable of the hall effect switch.